Owing to their distinguished semiconductor properties, AlN crystals are extremely useful as materials for creating a variety of semiconductor devices, including light-emitting devices, electronic devices, and semiconductor sensors. For this reason, growing large-diametric-span AlN crystals having superior crystallinity has become crucial.
Examples that have been proposed of how to grow such AlN crystals include a variety of vapor-phase growth methods, such as sublimation, hydride vapor-phase epitaxy (HVPE), molecular beam epitaxy (MBE), and metalorganic chemical vapor deposition (MOCVD). Among these methods, sublimation in particular is preferably employed, from the perspectives that the method can yield AlN crystal of favorable crystallinity and small full-width at half maximum in X-ray diffraction, and that the growth rates are high. Herein, “sublimation” means a technique in which crystal is grown by sublimating and afterwards re-solidifying the crystal source materials.
In sublimation, compound semiconductor substrates composed of compound semiconductors such as GaN and SiC are utilized as seed crystal substrates. Particularly, from the perspectives that the AlN and SiC seed crystals exhibit close lattice matching with the grown AlN crystals and that they have outstanding heat-resistance, AlN crystal growth on seed crystal substrates composed of AlN or SiC has been studied. (For example, cf. Non-Patent References 1 and 2).
In the above AlN crystal sublimation growth, producing large-diametric-span AlN crystals having superior crystallinity has been challenging mainly because areas in which AlN crystal does not grow (“crystal non-growth areas” hereinafter) are present on the AlN and SiC seed crystal substrates and other compound semiconductor substrates. Furthermore, particularly in the situation in which the SiC seed crystal substrate top is employed, the fact that the temperature at which the SiC crystals sublimate is 2300° C. is prohibitive of raising the temperature at which the AlN crystals grow, which has caused AlN crystal growth rates to drop.    Non-Patent Reference 1: V. Noveski, “Growth of AlN crystals on AlN/SiC seeds by AlN powder sublimation in nitrogen atmosphere,” MRS Internet J. Nitride Semicond. Res. 9, 2 (2004).    Non-Patent Reference 2: Lianghong Liu, “Growth Mode and Defects in Aluminum Nitride Sublimed on (0001) 6H—SiC Substrates,” MRS Internet J. Nitride Semicond. Res. 6, 7 (2001).